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Trouble bleeding brakes - soft on 1st press OK aft

I did a bunch of work on the car (98 528i sport MT) yesterday including rear pads, rotors, p-brake replacement, caliper rebuild, and bleed through from ATE Super Blue to ATE Type 200. (More on this later, I have some helpful hints and general rants)

I had no pedal issues going in, now the brakes are soft on first application but great on immediate reapplication. I know these are the same symptoms as for high rotor run out. I feel no vibration including braking up to 130kph and when the new parts were all mounted and I turned by hand there was even scuffing of the anti-corrosion coating all the way around the swept surface of the rotor - not ssh....ssh....ssh... I used Textar pads and COATED Balo rotors (my first time trying the coated).

For bleeding I used the old fashioned two person method with a brick under the brake pedal to limit travel. I don't think I made any mistakes - tapping the caliper piston with a rubber mallet occasionally (esp the rears which were taken apart), bleeding through until the colour changed and then the final couple of bleeds were at higher pressure, several open/close cycles (break bubbles free and squirt them out) and I didn't let the pedal bottom out against the brick to make absolutely sure no air was sucked in at the bleeder.

The only possible screw up I can think of is that after I drew most of the fluid out of the reservoir with a turkey baster I got interrupted and when I returned I set up the brick before adding the new fluid. I pressed the brake pedal onto the brick a couple of times by hand before I clued in and filled the reservoir back up. I know that "losing prime" in the master cylinder is a big problem but I didn't think I did and the entire bleed went completely routine (even the clutch) after that point.

Also I replaced the caliper slide boots on both sides. One of them was tough to get in but I don't think I mangled it permanently. It looked distorted for a bit but when I test fit the pin it was snug and felt like the other 3.

I know the first thing to do is bleed some more. I'm running low on the 1L of Type200 I bought and I can't get anything as good as that off the shelf around here. I know anything DOT4 is good enough but I'd like not to waste the expense on nice Type200 by following up with whatever house brand is at the local parts store. However if it was simply "bleed some more" I'm surprised by a second rapid brake application feeling fine - this isn't what I expect from bubbles.

I checked the fluid level after some driving and I haven't lost any. The brake pedal doesn't seem to fall when holding pressure (i.e. leak or torn master cylinder seal).

Any ideas other than bleed more? Anyone ever had bubbles cause the second-application-is-fine behaviour? Any chance my interruption mistake got a bubble into the ASC/ABS side of things that could have this weird effect?

Re: Trouble bleeding brakes - soft on 1st press OK aft

Craig,

I know you don't want to hear this, but you pretty much self-diagnosed your problem. When you used that turkey baster, and got as much fluid out as you could, there is not enough fluid in that reservoir to withstand even a partial brake pedal depressing. In other words, I'll bet a good dollar that it bubbled up, air rushed in, and when you released the pedal that air went into the MC. I had a friend who did something similar on his e39, and it took a lot more bleeding (in fact, we pumped the same brand in except that it was Dot 3 because when ran out of the Dot 4 stuff, which is actually fine since this guy is changing it yearly) to finally get the small bit of remaining air out. IIRC, only when I attached my Motive Pressure Bleeder and took it a few psi pounds past the recommended level, plus bleeding what seemed like too much did the pedal finally return to being firm on the first push. Hope this isn't it, so you don't have to waste your new Dot 4 fluid.

One thing I will say, is make sure you didn't just bleed the rears. Don't ask me why, but when doing any work like this ( at least on my car), if I only bleed the front and/or the rear, I get a super-soft pedal on the first push, then it hardens up on the second. Also, another thing: I know this sounds stupid, but when you bled the brakes, was the car off and/or running??

Re: Trouble bleeding brakes - soft on 1st press OK aft

I bled all four plus the clutch because it was a bleed-through fluid change. I also replaced a bleeder on the RF during the process but that didn't introduce any air into the system. It took 10s and it oozed from gravity the whole time I was working on it. The car was level (on stands) and not running.

I didn't go crazy with the turkey baster and I believe there was still fluid visible in the bottom of the res, dunno.

I went out and did more bleeding of the rears only this afternoon. Since I had them apart if there was air in the system not related to my MC screw up, it's most likely in the rear. Again I did the old fashioned method but this time with higher pedal pressure and lots more tapping with the mallet. I actually got a far bit of visible bubbles out although it's hard to be 100% certain what is just air in the rubber fitting I have on the collection tube and what really came out of the system.

On my test drive it was definitely better. The "two press" phenomenon was very distinct earlier today, not I'm waffling on whether it's still there or not.

I will shamefully admit that to conserve fluid I used my spotless clean bleeder collection doohickey and started pouring fluid back into the res. The whole system is only 1 day old fluid anyways, I'm just trying to eliminate bubbles. Not ideal, I know.

I think I'm going to monitor for a couple of days and see what I think. Maybe do even more bleeding when the snows go on.

The "two press" thing from air in the system really baffles me. I'd expect an always-soft behaviour if it was air. I'd love to hear and explanation. Unless, of course, it's a key LOCATION of the air (like MC, or MC connection into the ABS/ASC system or something).

I've read a number of very convincing statements from experienced folks which state that the old fashioned two person method gives the best bleed so that's what I've been doing. (Things about dislodging bubbles, flexing lines, pulsing the flow etc... compared to pressure or gravity bleeding). On the other hand if I have some MC bubbles you can't beat the convenience of a pressure bleed system to flow fluid in decent volume.

it sounds like u did everything right, and there

is no difference between a pressure bleeder and/or doing it the old fashioned way, imho, one way is just as effective as the other when done properly. It just sounds like you have "stubborn air bubbles" in there. I remember when I rebuilt my front calipers 3-4 yrs ago, I forgot to pour fluid (a trick advised to me by the BMW indie down the street) directly into the brake caliper while it is off the car (with the piston nearly out so lots of fluid would go in, then you hook the line back up, then you depress the piston until it goes on, and fluid will gurgle back into the brake reservoir when you do this). When I didn't do this, drove me nuts because after I assembled everything, I bled until I couldn't see straight with no air bubbles whatsoever, and still I had a soft pedal---but a it was a soft pedal. Finally, after lots of bleeding, I got the few remaining air bubbles out and the soft pedal was gone. Back then I refused to drive the car with any sort of soft pedal because it is too dangerous imho given the weight of the car & the speeds over here. Anyhow, good luck with it, you will get the last few bubbles out eventually. Other than a failing MC or run-out rotors (which doesn't apply to you), there is really no reason for a soft pedal except stubborn air bubbles somewhere in the system.

Eurodavid

P.S. the brakes are one of the things I love about BMWs, I feel really secure on the autobahn, as it is the best brakes I've ever had on a car in terms of "sure-feel" and the ability to stop the car

Re: it sounds like u did everything right, and there

Thanks, Euro. Even a "me too" story helps out with brake bleeding voodoo. By voodoo I mean I've read so many stories where people appear to do everything right but there's some stubborn bubble somewhere.

I was wondering - in the case that it is bubbles in the area of the MC, I guess the fastest way to handle that would have been lots of bleeding at the LF? No need to purposefully drag bubbles all the way through the car to the traditional RR first bleed point if you suspect you have MC-area bubbles, right? That would have been a good idea for me to have YESTERDAY :)

When reassembling the calipers I briefly thought about doing anything special and elected not to. My rationale was that I should keep the air pocket trapped near the bleeder instead of risking pushing it back into the system and making it harder to get out. That worked well *facepalm*. I think that the higher pedal pressure and lots more mallet-tapping make it work better the second time.

On brake feel/performance - I've never been that thrilled with any E39 I've driven (at least 5). Even when in tip-top shape I've found the pedal soft. It stops the car, but it's not "sporty". If you were really driving the car hard (like on track braking from a straight into a hairpin) I think the brake pedal would end up so far below the accelerator you couldn't heel/toe rev match downshift very well. Every E46 I've driven has a significantly better pedal feel by comparison.

Some of the nicest I've driven (which doesn't say much) are Porsches with four pot calipers on all four corners. My 968 was set up this way and the pedal was really hard and easy to modulate - one of the things I love about fixed-piston calipers over floaters like we have. A couple of 911s I've driven were really fun too because the rear-heavy weight distribution approaches 50/50 on heavy braking so the rears do as much braking as the fronts - unlike most other cars. In my salty environment I'm not going to try things like the brass slide bushings to try to stiffen things up. I know there are some quality stainless lines out there, but I gave up on that DOT-questionable stuff long ago after reading about all of the failures. My 968 was all stock and didn't need those band aids to have great feel. I've never driven any of the 6 or 8 pot variants. I wonder if E39s with StopTech setups have rock hard pedals or if there's other flex in the MC and lines which contribute to the relative "softness".

Two day update

As I said, I went back out Sunday and did a bunch of bleeding from the rears using more pedal pressure and way more mallet tapping and I think I got a bunch of air out.

On my test drive I thought the situation was much improved but there was still a subtle two-press effect. Driving the car last night it seemed a little more prevalent to me and today my wife says she thinks it's about as bad as before.

Tonight I'm going to put all four up in the air again and do a ton of bleeding from the LF to start - in case bubbles are near the MC. I think I'm going to do a little bit of something less traditional too. I'm wondering if bubbles aren't somehow getting pushed into passes to the ASC/ABS or something. Between brake applications they work their way into the common circuit somewhere. First pedal press they get shoved down some other passage and second pedal press you have no bubbles in the main loop. Just a wild theory possibly explaining the "two press" behaviour.

I'm going to try doing a little bit of LF bleeding (least tubing from MC to bleeder) where I open the bleeder before the brake is applied, and then hit the pedal. I'm hoping any bubbles anywhere near the MC will follow the path of least resistance down to the LF bleeder instead of into any other nooks and crannies. Then I'll return to normal practices and bleed all four with extra mallet taps and higher pressure.

We'll see what happens. I really don't want to have to drag this to a shop just to activate the ASC/ABS loop and bleed it for me.

I you're going to do this more than once>>

in your lifetime, get the Bav Auto pressure bleeder. It's more positive than up-down, up-down, and it's easier on the master cylinder, esp if there's a ridge at the end of the stroke, which can damage the piston seal.
Ed in San Jose. BMW CCA member since 1987 (Nr. 62319). Golden Gate Chapter. '97 540i 6 speed. Build Date 3/97. Aspensilber over Aubergine leather.

I've been using the BAV pressure bleeder since (m)

day 1 and don't have any problems bleeding. Didn't have them in the old days either when I had to borrow my wife's foot to do the pumping.
Craig, if you think you have air in the ABS take the car for a drive on a wet road and get the ABS to function. That will push out any bubbles that you think may be in there.
OH WAIT, take the hood off and have the wife beat on the ABS unit while you activate it to loosen any bubbles in there.....bet you already thought of that. (just razzing ya)

This is what I would do...

Good day!!

I agree that the ABS should be engaged to move the fluid around and possibly get the air to move (if there is any)... So, I would try this...

Jack up all four corners. Pull the wheels and calipers. Push the pistons back in on all four corners... Take care about the level in the MC!!!! Don't want that stuff to over flow on your paint! With all pistons pushed in, re-install all calipers. Start the car, and let the vac build up. Turn off DSC/ASC and move into D or 1st. Get the rears turning very slowly! Slam on the brakes. This should NOT stop the wheels from spinning, but it should force any air into the lines instead of sitting in the areas it can collect. Let up on the pedal and press again, but slower as the brakes may start to grab this time... The ABS should engage both times as the fronts aren't moving, but the rears are (VERY SLOWLY)! Once you have a good pedal pressure, re-do bleeding procedure you did before...

I always reuse new clean break fluid that made a complete passage thru the brake system... I don't see the point in wasting good fluid...

Results of this attempt

As I mentioned, I bled a lot from the LF, then did a standard sequence of RR, LR, RF, LF again.

@william540i: I may try that ABS activation trick. I have some vague recollection of someone mentioning that you could simply jumper the ABS pump and it would circulate. I'm not sure if it would circulate or just build excessive pressure in an accumulator somewhere. Anyone remember anything like this?

@edjack: Yes, it might be time for a power bleeder.

My observations from last night:

What I noticed from the first LF bleeds is a good number of TINY bubbles in the fluid - the kind that seem to stay put exactly and not move at all.

I think I got some "regular" air out of the RR AGAIN. The LR and RF didn't have much of anything going on but I moved at least a cup or two of fluid through each. Occasionally one of those tiny bubbles was visible but not much at all. Returning to the LF there were still some tiny bubbles and I bled about 750mL through until they were nearly gone. Before pouring fluid back into the reservoir I thumped my collection container with a mallet a lot to try to get the tiny bubbles out of suspension since pouring them back in isn't going to help me.

So, I'm not sure what's up with the tiny bubbles. Whether they're being torn off of a larger air pocket somewhere like the MC or what. I'm ordering a RR wishbone so I ordered a 1L can of ATE SL DOT4 which is the same price as, but better than, the stuff at the local parts store. I won't graduate to Type200/Super Blue until I know it's fixed.

On the test drive it's definitely improved again but the two press is still there. Something like 2.5L of bleeding and still - argh!

Interesting performance results though. The pedal height feel on the first press is almost as good as before I did the brake job but the stopping power is better when you give the pedal a goose. When you do a double press HOLY MOLY. Now that the new rears are scuffed in a little I've never had braking like this before, even after the dealer did my last full F/R R&R. It was around freezing out and there was dust and dirt in my test area and my PS2s still didn't run out of grip despite how incredibly fast I could stop. It is as if the car lost 1000lbs and everything else stayed the same.

My rears were working before, but clearly not fully effective. This goes to demonstrate what a role the rears still play in overall performance. I'm sure this is driving Eurodavid mad :)

Despite it not being fully fixed I'm confident in the car's stopping power for a couple of days while I sort out what to do next. I want every pedal press to be like last night's second press. Until there's snow and ice on the ground I can't activate the ASC/ABS the normal way - I drive an I6 with PS2s. I'm not too excited about finding a gravel test track and my neighbours don't want me on their lawn. Generally I don't bother cycling the ABS as part of a change because I buy "3 year" fluid and change it yearly-ish. In the winter I made sure to cycle the ABS system a bunch when opportunity presents itself and I consider it flushed. Once the summers are on, I don't think ABS wakes up from March to November.

I usually try to activate my ABS weekly...

Not for a long time, cause I'm taking life off the tires, but just enough to get the ABS to kick in, then release...

I did a brake job on the ex's 540i sport, and it was night and day difference compared to my car (we HAD twin black 98 540i/6's)... I think I used Axxis pads on hers... I worked the caliper pistons thru it's operating range before seating them with the new pads... No hang-ups on any caliper so I left it alone... I did a recent front brake job on mine, but had to go with the cheapo pads from advance auto (tight budget back then ~ divorce was still pending), and I hate the braking performance... I want to get the best braking pads made, regardless of dust, but still be in daily-driver temps... I don't plan on taking my car to Nurburging often, but maybe once or twice a year, after I get there...

Please make sure you use extreme caution when engaging the ABS on the stands... Newtons law of motion suggests that for every action, there is an equal and opposite reaction... You stop the driveline from say 15-20 to zero in a split second, the car is gonna respond... Make sure the brakes are gonna SLOW the driveline... The ABS will [read: should] automatically kick in just cause the fronts aren't moving from the beginning... BLOCK the front wheels, double support the rear and remove the tires to lower the rotational mass...

I think it would be much safer and easier to find(

I agree!! The main thing in my option is getting

the piston in the calipers pushed in to force any bubbles back to the resevoir, then forcing the rest thru the system as the pistons re-seat the pads... I guess you don't have to have the trans in gear to do that... It was only an additional thought to engage the ABS while you were there... Any bubbles that move downstream will stay put cause there is no back pressure on the pistons... Once in the lines, regular bleeding should clear them out...

Safer is better!!! Maybe do the wet road ABS thing first, then see what happens...

Re: Results of this attempt

I wonder if you could look in Bentley for pin schematics of the ABS pump wiring connector and jump appropriate pins. You'd really have to what you doing before attempting that. I also think that air is trapped in you ABS pump.

Update: 4th bleed

So today I recirculated about 1.5L of fluid from all bleeders, then did a turkey baster extraction from the reservoir and started on the new 1L container for ATE SL.

I also followed some of the advice here and retracted the calipers before starting in order to get a little bit of a flow back into the reservoir first.

When I started I noticed a lot fewer tiny glittery bubbles in stream than the last bleed. I wanted to run the fluid in a circle until I saw almost none and then start on the new stuff. I don't think I found any "traditional" air anywhere in the system just these dang glittery bubbles.

What I noticed is that if I open the bleeder slightly, they would put a thread of these glittery bubbles into the fluid in my bleeder lines. If I opened them wide you couldn't really see it. This would happen every time I slightly opened them even if the brake pedal was not released and pressed again.

If I had to give an opinion, I would say that the RR and LF had the most of this going on. Does the E39 have an X-split system like other cars I've had? Where there are two circuits that criss-cross in case there's a line failure or something in one you still have the pressure in the other? I wonder if that could be a pointer to where these bubbles are coming from.

I bled pretty much the whole liter of new fluid through and I could still get these fine threads of tiny glittery bubbles in the stream. You have to have your face in the wheel well and have a shop light shining through the tube to see them.

On my test drive I'd say that the brakes are again improved. Overall they're better than before my rear brake job but the second press still seems better than the first in a lot of cases (but not all) - slightly higher and firmer pedal. I have to say that other than the double-press - if someone had done this to my E39 without telling me I'm not sure if I'd notice any change.

For the record, when the fluid was low in the reservoir, I had my wife apply the brakes with the system closed to see if there was much of a suck/pull and change in level. There was not. I have my doubts as to whether I actually ever sucked air into the MC in the first place since I didn't get anywhere near draining the reservoir dry when I made my little mistake during the brake job.

So, I ponder the following:

1/ Maybe I don't have a new problem. Maybe there's runout in the older front rotors which I can't feel yet when stopping? Or maybe there's some kind of problem in the system leading to the two press behaviour that was there before - I just wasn't playing around with double application before.

2/ Maybe I have no problem (at least not with the car) at this point. Earlier on I had "typical air" in the line from the rear caliper seal change which took a little while to be totally removed from the system. Now that's fixed and I should stop obsessing. I'd really like that second-press braking performance though.

3/ Maybe there's air or some kind of system problem in one branch of an X-split system, if the E39 has something like that, explaining the RR/LF bubble factor. I have done a LOT of LF bleeding because it's close to the MC.

3a/ Maybe there's still something in the ABS/ASC circuit. I activated ABS today on the test drive since it was damp out. It worked fine, no codes or lights, but it wasn't on for very long. I need snow/ice to get a long run.

4/ Where do these micro-bubbles keep coming from? I realize that 10,000 microbubbles are as bad as one big bubble so I assume that they're relevant. If I take the car to a shop what more are they going to do for me other than maybe use a power bleeder and run a couple of liters through (which I've effectively already done)? Has anyone ever heard of recurring micro-bubbles as a diagnostic condition?

5/ Is there an MC wear condition that would create double-press behaviour or micro-bubbles? I don't want to embark on MC replacement just for the heck of it. I have no falling pedal, or leaks evident anywhere.

Doesn't the second pump on the brake pedal (m)

always better than the first? The first pump moves the pads out to the rotors. When you take your foot off the pedal the pistons do not have time to retrace all the way back to their rest position. Then you pump it a second time, the pistons/pads have less distance to travel so the brake pedal doesn't have to move as far.....the brakes feel like they are working better.
That's my guess and I'm sticken to it.

Not to change the topic, how long did it take you to pull the dash off on your Dad's 540?

Re: Doesn't the second pump on the brake pedal (m)

Well, the thing with that is that disc brakes are "zero clearance". They are only pushed away from the rotor by its spinning action - they don't retract. This is why "better on the second push" is usually a sign of rotor runout or bad wheel bearings because the wobble at the caliper actually DOES push the pads farther out than zero clearance.

I just don't see any other signs of runout happening anywhere, and runout doesn't explain the micro-bubbles in the fluid. It doesn't take much time, like 5 seconds off the pedal even at 20mph to allow for a second-push-is-better behaviour. I don't have to load up the wheel bearings or anything and if my rotors had that much runout I should have wicked shaking during high speed braking and I don't. Stumped...

On the dash, probably 5 hours total but a good 1.5h of that AT LEAST was wasted fooling around with things that were different from all of the instructions or where instructions (Bentley, TIS and writeups) could have been clearer. I intend to make a separate thread about that in hopes of saving someone else a bunch of time. A second time would be much faster. We weren't rushing in the slightest either, and I was wiping down and polishing or applying protectant to everything as I reassembled it. In retrospect, someone who's done it before should nail it in under 2h, I would almost think.

just drive the damn thing for now...

I know your frustration and obsession very well :-) been there done that. Drive it for a week and try and not concentrate on the brakes. Ask somebody else to drive it... if there is a trouble, they will notice it if not then you imagine things.

I had bad (or so I thought) bakes on my 840 for a while, until I drove a few others. Then I realized they are all crappy. There is no vacuum booster on the E31 but a vacuum pump. Horrible design, kind a like the GM Hydro-boost. Delay in pedal action and long pedal travel, more pedal force needed, etc.

I bled the whole system out with fresh DOT4 fluid and all is better. So much better, I actually got used to it.

Then I got into the E39 which has crappy rotors on the front and WOW !!! The thing grabs and brakes with ease. The E31 feels crappy again...

so believe me some of this trouble with the car is in out head.

ps. Today I flushed my Wife's Mazda CX9's brakes. Again, the brakes on the BMW's are crappy compare to that thing... it amazes me how good the Mazda brakes (Ford calipers and stuff) are. Perfect pedal travel, perfect pedal pressure, brake is extremely strong and easy to modulate, etc.